Electron-density dependence of line intensities of Cu I-like Sm33+ to Yb41+ emitted from tokamak and laser-produced plasmas.

Abstract

The density dependence of \ensuremath{\Delta}n=0 (4-4) transitions for rare-earth-metal ions isoelectronic with Cu i has been studied over a large density domain ${10}^{13}$--${10}^{21}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ by measuring the spectral emissions from these ions in tokamak and laser-produced plasmas and comparing them with theoretical models. The computational techniques used for the atomic parameters in the collisional radiative model of the level populations were checked in the low-density range \ensuremath{\sim}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ by analyzing the spectra of ${\mathrm{Eu}}^{34+}$ and ${\mathrm{Yb}}^{41+}$ emitted from a tokamak plasma. Then laser-produced spectra of ${\mathrm{Sm}}^{33+}$ and ${\mathrm{Yb}}^{41+}$ were analyzed using similar models for the density dependence of the line ratios in the high-density region ${10}^{19}$--${10}^{20}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. The theoretical models included the effect of cascading from n=5 states on the population of the n=4 levels. In addition, optical depth effects on the line intensities were considered for the high-density laser-produced plasmas. The present work demonstrates the potential of highly ionized rare-earth-metal atoms as electron-density diagnostics in high-density plasmas. In particular, all along the isoelectronic sequence from Z=59 to Z=70 the two density-sensitive transitions 4d $^{2}D_{5/2}$--4f $^{2}F_{7/2}$ and 4p $^{2}P_{3/2}$--4d $^{2}D_{5/2}$ remain close to each other and are unblended with other lines, and thus their ratios represent particularly attractive density diagnostics.